Abstract

This study on the effects of paternal and maternal goat size on kid growth
and survival was conducted by grouping bucks and does into big/elite and
small/control categories and mating between the sub-groups to create four
progeny groups whose body weight and mortality rate were assessed for fixed
and variable effects at birth, 10, 20, and 30 weeks of age.

Big sized bucks and does had progeny that were heavier than those of small
sized parents at all ages except at birth. The mean body weight of the
progeny at 30 weeks was 15.1±0.6 kg for elite bucks and 13.2±0.8 kg for
control bucks. Due to sexual dimorphism, male progeny were heavier
than their female counterparts at birth, 20 weeks and at 30 weeks. Birth
type had the most profound effect on both live weight and survival of goats.
Single kids weighed 2.2 ± 0.05 kg at birth compared to 2.0± 0.03 kg for
twins, and the margin of superiority widened to 3.5 kg at 30 weeks. Over 85%
of the kids that died between birth and 30 weeks were born as a twin which
effectively negated the advantage that is normally thought of for twinning
in such a goat flock.

It is concluded that paternal and maternal size influences the weight of
progeny at birth and through to maturity. Birth type and sex of kids also
have profound effects on kid weight as well as on survival. However, the
advantage of elite parentage appears to get diminished unless diet
improvements are incorporated. In general, using elite bucks does have
potential financial benefits for Mubende goat farmers.

Introduction

Livestock production is increasingly being driven by a shift in diet and
increased food consumption of livestock products (FAO 2013). Over the past
few decades, most of this shift has been observed in developing countries
(Mugisha et al 2009). Goats, by their nature, continue to be of potential in
many areas but are usually not targeted by livestock research for
development. Small ruminants, like goats, should be the animals considered
for small farms in developing countries due to their small size, ease to be
fed, housed and treated when sick. Their small size also makes it easier for
households to slaughter and consume piece meal without worry for prolonged
meat preservation as is the case for bigger livestock species.

In 2010, out of the world’s two billion sheep and goats, over one third was
in Africa and one half in Asia (FAO 2013). Despite these population
statistics, the actual consumption of meat in the developing world is still
very low and the predicted livestock revolution (Delgado et al 1999) may not
materialize at the level predicted due in part to the private sector not
supporting the opportunity to increase livestock production. To meet the
continuously increasing demand for both milk and meat in the developing
countries, improvement in livestock productivity is still very much needed.
Such improvements could be realized through a combination of improved
husbandry and careful utilization of the existing livestock genotypes
(Philipsson et al 2006), including both selection within breeds and
orderly/planned crossbreeding. Selection only works where there is
variation, and the wider the variation, then the more likely that selection
will succeed.

Phenotypic variation in a population is a result of a number of factors such
as the individuals’ genotype, environment, or an interaction between the two
(Plomin et al 1977). The environment may influence an individual’s phenotype
directly or through environmental effects associated with its mother
(Rossiter 1996). These environmental effects on the offspring are a result
of the dam’s genotype for traits like milk production, and are usually as a
result of the environment experienced by the dam (Freeman et al 2013). Among
other effects, maternal nutrition plays a critical role in foetal growth and
development in most livestock species (Wu et al 2004). This study was conceived, after observing that among the Mubende goats
(Photos 1 and 2), a wide variation in weight/size exists between goats of
the same age and that there is a financial advantage to smallholders in
rearing bigger goats. This means if big bucks and does could produce faster
growing progeny than their smaller counterparts, it would make economic
sense for farmers to invest in bigger bucks and/or bigger does. Therefore,
the objective of this research was to determine the effect of paternal and
maternal body size of Mubende goats on growth and survival of their progeny.

Materials and Methods

Study site

The experiment was conducted at the Makerere University farm (0o
28’N, 32o
37’E), located 20 km north of Kampala City in Uganda, at an altitude of 1250
m at the highest point and 1185 m in the valley bottoms. The annual rainfall
is about 1300 mm for an average of 150 rain days. The wet season includes a
broad peak in March to May and a narrow peak in October to November; the
wettest months being April (+200 mm) and November (+180 mm).

Experimental Animals

Sixty does and six bucks were selected from a goat flock of 100 goats,
excluding pregnant, lactating and goats with compromised health. Using chest
girth and live body weight, the goats were grouped into big size (elite) and
small size (control) (Table 1). Three elite bucks were mated to 15 elite
does and 15 control does, while three control bucks were mated to 15 elite
does and 15 control does. The mean chest girth of the does at mating was
78.4 ± 0.7 cm (elite does) and 72.2 ± 0.6 cm (control does); while the live
weights were 35.9 ± 0.6 kg (elite does) and 28.4 ± 0.4 kg (control does).
For the bucks, the mean chest girth at mating was 81.4 ± 0.4 cm (elite) and
67.8 ± 0.4 cm (control); while the live weights were 41.6 ± 0.2 kg (elite)
and 26.6 ± 0.3 kg (control). A total of 75 kids were born; 20 single, 26
sets of twins and one set of triplets.

Table 1: Categories of goats used in the study

Goat category

Level

Number of goats

Live weight (kg)

Chest girth (cm)

Elite/Big

Elite Buck (EB)

3

>40

>80

Elite Doe (ED)

30

>33

>76

Control/Small

Control Buck (CB)

3

<35

<78

Control Doe (CD)

30

<32

<76

Housing and holding system

All the goats were managed under the semi-intensive system in which housing
was basically for overnight occupation by the various goat groups while most
of the day time was spent outdoors. Does and weaned goats were kept
overnight in raised and slatted floor pens with an average floor space of
1.5 square meters per mature doe and one square meter per weaned goat.
Lactating mothers were housed in ground-level slatted floor pens with over
3/4 of the walls covered to avoid draughts. The rest of the houses had walls
made of timber boards, with wire mesh covering the upper 1.5 m of the walls.
Bucks were housed in a permanent house with wooden slats floor. A yard of 9
m × 15 m constructed with a concrete floor was used as a mating area for the
goats.

Feeding and health management

Does and weaned kids were grazed daily on open pasture. The predominant
grass species were Guinea grass (Panicum maximum), Rhodes grass (Chloris
gayana), Foxtail (Setaria anceps), Star grass (Cynodon dactylon), and Signal
grass (Brachiaria brizantha). A fenced paddock measuring 40 m × 50 m near
the holding/housing unit was used for late afternoon/evening grazing. Bucks
were usually tethered on good pasture and sometimes allowed to graze in the
paddocks. The grazing of both does and bucks was occasionally supplemented
with fresh leguminous fodder of Leucaena leucocephala and Gliricidia sepium.
Water was provided ad libitum to the goats in the holding/collecting yard.
Mineral salt licks were given fortnightly.

All goats were provided with treatment as and when they showed signs of
sickness. Predominant diseases encountered included diarrhea (scours) and
pneumonia in kids; mange and wounds in mature goats. Worm and fluke
infestation was also recorded especially in the rainy season. Drenching with
anthelmintics was done bi-monthly in the mature herd, and monthly among kids
and weaned kids (weaners). Other less frequent health problems encountered
included foot rot and milk fever. Bi-weekly spraying of the goats with
acaricides ensured control of ecto-parasites like ticks, lice and fleas.

Data collection

Kid weights were taken using a 20 kg range Salter® scale, before 0800 hour,
taking care to avoid weighing them after suckling or after exposure to other
feed. Each kid was individually placed in a polyethylene bag which was
suspended onto the scale. Measurements were taken weekly starting at birth
until 52 weeks of age.

Data analysis

Simple means and ranges were computed across the entire data set and by each
class variable to identify data entry errors. Data were subjected to analysis
of variance using PROC MIXED procedure of SAS Ver. 9.2 (SAS 2012). The
model used included buck size category (Elite or Control), doe size category
(Elite or Control), birth type (single or twin), the interaction between
buck and doe size classification, and sex of kid were included in the model
as fixed effects and doe number was included as a random effect. Least
square means for each level of all fixed effect classifications were
estimated. The dependent variables evaluated included kid birth weight,
10-week body weight, 20-week body weight and 30-week body weight. Not all
animals were represented at each weight point due to mortalities that
occurred. Mortality records (alive or dead at end of 30 weeks) were recorded
and analyzed using only simple descriptive statistics because of the limited
information available for these traits.

Results

Big sized bucks sired kids that were not different (P>0.10) in birth weight
from those of control sized bucks (Table 2). However, the elite buck effect
was significant (P<0.01) at 10 weeks and tended towards significance
(P<0.10) at subsequent ages. Kids mothered by elite does followed a trend
similar to that of their counterparts sired by elite bucks. Birth weight of
kids was significantly influenced (P<0.01) by their sex and birth type. Male
kids were superior (P<0.01) to females at birth and at all post-weaning
ages. The effect of birth type was the most intense in this study, with
single kids weighing significantly (P<0.01) more than twins at birth, 10
weeks, 20 weeks and 30 weeks.

A total of 28 kids (37.3%) had died by the age of 30 weeks. The mortalities
occurring up to 30 weeks of age may have been influenced by doe size, with
75% of the mortalities being for kids born to control does, while only 25%
were by elite does. Only 42.9% of the dead kids were sired by elite bucks,
and 57.1% of kid mortalities were sired by control bucks. A combination of
small-sized parents caused 46.4% of the mortalities while only 14.3% of the
mortalities resulted from mating both big-sized bucks and does. The mating
of elite does to control bucks resulted in less kid mortality (10.7%) than
when control does were mated to elite bucks (28.6%). Most of the kids that
died (57.1%) were male. A greater proportion (85.7% ) of the kid mortalities
were born as one of twin kids, while only 14.3% of them were born as a
single kid. While kid mortality was not
evaluated in depth, the trends identified using simple statistics are
suggestive to the impacts from differing buck and doe size.

Discussion

It is important for this discussion to understand that the purpose of this
study was to investigate the role that parental body size, litter size and
kid sex has on growth performance of Mubende goat progeny. Mubende goats are
one of the four goat breeds in Uganda. Considering their relatively big
adult body size (Semakula et al 2010) and national flock size, it is the
breed that should be contributing most to the goat meat consumed in the
country. It is therefore imperative that performance of this breed is
enhanced and this study was conducted so as to contribute to that
enhancement. Awareness of how breeds and breed combinations compare for
economically important kid traits from birth to weaning allows for diversity
present to be exploited by proper breed selection (Browning and
Leite-Browning 2011). In this study, focus was on the diversity in body
weight of mature Mubende goats such that if a genetic basis of size is
determined, selection could be promoted.

Buck and doe size effects on progeny growth were significant or tended
towards significance over the 30 week period (probably ranges from P<0.01 to
P<0.10). This observed superiority can be explained by the concept of
genetic size and growth in goats (Ogink 1993). Accordingly, genetic size is
expressed during the developmental stages of growth and it peaks in the
mature animal. Offspring from Elite does were not different at birth
however, at 10 and 20 weeks they tended to be heavier (P<0.10), and
at 30 weeks were heavier (P<0.05) when compared to offspring from control
does. As showed in Table 2, sex and birth status (single/twin) were
significantly important effects at 30 weeks (P<0.05), with males showing
superiority over females; while single kids grew faster than twins
throughout the study period.

The mean birth weight of Mubende goats in this study (2.1 kg) is close to
previous studies showing 2.0 kg (Oluka 1999), but much higher than 1.22 kg
(Okello 1993). Birth weight is an economic trait, which has a positive
relation with kid survival and overall post-natal development. The
heritability estimate of birth weight in goats ranges between 1.5% and 46%
(Roy et al 1989; Das et al 1996).For the reason that these values are low to
medium, genetic progress in improvement of meat production through selection
procedures based on birth weight is relatively feasible. Birth weight is an
indicator of the rate of fetal growth, itself regulated by genetic,
epigenetic and environmental factors (Ashworth 2013). These factors
influence placental growth and functionality, and ultimately, the maternal
uterine environment particularly size and efficiency of the placenta. Within
a given breed, birth weight depends on the weight of the parents and
especially the adult dam weight (Berhanu et al 1991) and its age (Das 1993;
Browning and Leite-Browning 2011).

Male kids were superior (P<0.01) to females due to the effects of
sexual-size dimorphism (Shine 1989; Liao et al 2013) which is widely
observed in the animal kingdom, appearing commonly in domesticated as well
as wild species. In domestic mammals, human control replaces sexual
selection that is found and plays the dominant role in the wild mammals
(Fairbairn 1997; Zhang and Lu 2013). In wild mountain goats, the inheritance
pattern of this unique attribute has been extensively studied (Mainguy et al
2009), and shows that superiority in size is actually genetic. In the
current study, more male kids (1.33) died per female kid, implying that sex
could have been of influence on survival, as was found in goats elsewhere
(Perez-Razo et al 1998).

Birth weight decreased as litter size increased (Table 2), with single kids
growing much faster than twins at all ages. The relationship between single
and multiple births has also been documented with other breeds such as Boer,
Kiko, and Spanish (Browning and Leite-Browning 2011). Indeed, while the
weight differential between single and twins in the current study was 0.2 kg
at birth and 2.3 kg at 70 days, it was 0.4 kg at birth and 2.9 kg at 90 days
in Boer and Spanish goats (Browning and Leite-Browning 2011). A life-history
trade-off between offspring number and size has recently been documented
(Schroderus et al. 2012) and apparently, the heritability of litter size is
low in most litter producing livestock such as goats (Menendez-Buxadera et
al 2003), rabbits (Rastogi et al 2000) and swine (Holl and Robison 2003).The
superiority of the singles’ live weight over twins could be explained by the
higher nutrient uptake per kid expected for singly born kids. It is probable
that single kids consume more colostrum and hence more immunoglobulins than
twins or triplets. This means that resistance to disease is stronger in
singles and hence the higher possibility of a better growth rate, live body
weight. This should also explain why the mortality ratio between singles and
twin over the 30 weeks studied was 1: 6. According to Robinson et al (1977),
as the number of fetuses in utero increase, the number of caruncles attached
to each fetus reduces. This therefore reduces the nutrient uptake for
offspring raised in big litters. Elsewhere, litter size and parity were
found to be responsible for 28% of the variation in birth weight in West
African Dwarf goats and a bigger 46% of the variation in Saanen goats (Ogink
1993).

Mortality of goat kids has been shown to be associated with birth month,
litter size at birth and dam age (Browning and Leite-Browning 2011).
Mortality rates have been shown in previous research to decrease as litter
size increases while on the other hand; sex of kid did not influence
pre-weaning survival (Browning and Leite-Browning 2011). In our study, the
goat flock showed a characteristic low pre-weaning mortality rate of 13.3%,
compared to 17.0% (Okello 1993), and 20.3% (Oluka 1999) who also worked with
the Mubende breed. Boer goats raised in Uganda were found to have a
mortality rate of 11%, and a similar value was documented for the Small East
African goats (Nsubuga 1996). Work done by Sacker and Trail (1966) and
Wilson (1982) reported that mortality rates among Ugandan goats are
characteristically lower than those reported for other African studies. This
could be a factor of disease adaptation and not necessarily health
management as may be surmised.

Of particular concern is the question of whether the variation between
progeny of the two parental groups could have been broader if the diet,
which was limited to naturally existing pasture grasses, sparse legumes, and
occasional legume fodder, had been supplemented with more dietary protein.
The probable answer is positive. The adverse environmental conditions under
which indigenous animals are reared have for many years limited the attempts
to improve livestock productivity in most developing countries in the
tropics (Katule 1991) and when this is coupled with low genetic potential,
the situation does not get better. Clearly the overriding question is, will
improved genetics express themselves without improved feeding and other
environmental conditions? The response according to our findings is
negative.

Implications of these findings are that smallholder farmers must determine
the value of buying improved (elite) bucks at increased costs. Considering
that an elite buck cost $100, while small bucks cost $60 and that when
selling goats, farmers receive about$2.5 per kilogram of weight; using an
elite buck at a mating ratio of 1:30 would produce at least 50 animals in
the flock. This would potentially increase the flock off take per annum by
$340. Clearly, it would offset the $40 price differential between elite and
control bucks.

Conclusion

Paternal and maternal size does influence weight of progeny at birth and at
subsequent ages. Birth type and sex of kids also have profound effects on
kid weight. However, the advantage for producers to use elite parentage is
not completely realized through increased kid weight. This may be the result
of inadequate nutritional resources for both the dam to produce sufficient
milk and the offspring to reach their genetic potential for increased weight
gain.

Recommendations

The following recommendations have been formulated for ensuring increased
growth performance of Mubende goats:

Big bucks should be promoted for use in goat breeding since they show
genetic elitism

Improving post-weaning diets of goats is pertinent so as to actualize
the growth superiority resulting from use of elite sires and dams.

Acknowledgements

The Centre for Sustainable Rural Livelihoods (CSRL) and the College of
Agriculture and Life Sciences (CALS) of Iowa State University and the
Ensminger Endowment in the Department of Animal Science are acknowledged for
providing a visiting scholarship to one of the authors (D R K) during which
the manuscript was developed. The authors thank the management of Makerere
University farm for allowing this study to be conducted. Comments by the
editor and reviewers were very helpful.

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